The technical portion of the work carried out by an optician consists in mounting a pair of ophthalmic lenses in or on the frame selected by the user, in such a manner that each lens is suitably positioned facing the corresponding eye of the user so as to perform as well as possible the optical function for which it is designed. In order to do this, it is necessary to perform a certain number of operations.
After the frame has been selected, the optician must begin by situating the position of the pupil of each eye in the frame of reference of the frame. The optician thus determines mainly two parameters that are associated with the morphology of the user, namely the pupillary distance and the height of the pupil relative to the frame.
For the frame itself, it is necessary to identify its shape, and this is generally done by means of a pattern or an apparatus specially designed to read the inner contour of the rim (i.e. the part of the frame that goes round the lens), or else from an electronic file that is prerecorded or supplied by the manufacturer.
From the above geometrical input data, it is necessary to cut each lens to shape. A lens is cut to shape for mounting in or on the frame selected by the future user by modifying the outline of the lens so as to match it to that of the frame and/or to the shape desired for the lens. Cutting to shape comprises an edging operation for shaping the periphery of the lens, and depending on whether the frame is of the rimmed type (the frame then has rims with inner bezels forming grooves), or of the pierced type (a frame having no rims but with point clamping through fastener holes formed in the lens), or of the grooved type (with a frame possessing firstly two top half-rims each presenting a bevel instead of the bezel of rimmed frames, and secondly a nylon string that goes around the bottom portions of the lenses), cutting to shape also comprises appropriately bezelling and/or drilling and/or grooving the lens. Edging (or cutting out proper) consists in eliminating the superfluous peripheral portion of the ophthalmic lens in question so as to reduce its outline, which is usually initially circular, to the arbitrary outline of the rim or surround of the eyeglasses frame in question, or merely to the pleasing shape desired when the frame is of the rimless type. This edging operation is usually followed by a chamfering operation which consists in dulling or chamfering the two sharp edges around the edged lens. When the frame is of the rimmed type, the chamfering is accompanied by beveling which consists in forming a rib usually referred to as a bevel, generally of triangular cross-section with a top that is rounded or interrupted by a counter-bevel on the edge face of the ophthalmic lens. The bevel is for engaging in a corresponding groove, also known as a bezel, formed in the rim or the surround of the eyeglasses frame in which the lens is to be mounted. When the frame is of the rimless type, the cutting out of the lens and optionally the dulling of its sharp edges (chamfering) are followed by appropriately drilling the lenses to enable it to be secured to the temples and to the bridge of the rimless frame. Finally, when the mounting is of the type having a rim of Nylon string, the chamfering is accompanied by grooving consisting in forming a groove in the edge face of the lens, the groove being for receiving the mounting Nylon string for pressing the lens against the rigid portion of the frame.
Usually, these edging, chamfering, and beveling operations are performed in succession on a single machine tool, known as an “edger” and provided with a set of suitable cutter/edger bits. Drilling can be performed on the edger which is then fitted with corresponding drill bits, or else on a separate drilling machine.
The optician must also perform a certain number of measurement and/or identification operations on the lens itself prior to cutting out in order to identify certain characteristics such as, for example: the optical center if the lens is a single-vision lens or the mounting cross if the lens is a progressive lens, or the direction of the axis of progression and the position of the centering point if the lens is a progressive lens. In practice, the optician marks certain characteristic points using a marker tip on the ophthalmic lens itself. These marks are used for securing a chuck receiver or centering-and-drive pad on the lens enabling the ophthalmic lens to be positioned correctly in the edger that is to give it the desired outline, corresponding to the shape of the selected frame. The pad is usually stuck temporarily on the lens by means of a double-sided adhesive. This operation is commonly referred to as “centering” the lens, or by extension, “blocking” the lens, insofar as the pad can be used subsequently for blocking purposes, i.e. for preventing the lens from moving relative to the means for cutting it to shape in a geometrical configuration that is known because of the pad.
Various devices are known for measuring and identifying or centering, which devices operate either automatically or manually, in order to measure various characteristics, and in particular centering or identifying a single-vision or progressive ophthalmic lens before or after it has been mounted on a frame. In particular, one such device is known from document FR-2 825 466 and its equivalent US-2003/0015649, published on Jan. 23, 2003.
After the centering pad has been put into place, the lens fitted therewith is subsequently placed in a cutting-out machine where it is given the shape corresponding to the shape of the selected frame. The centering pad serves to define and physically embody on the lens a geometrical frame of reference in which characteristic points and directions of the lens are identified, as are required for making it match the position of the pupil, and also making to possible to define cutting-out values so that these characteristic points and directions are properly positioned in the frame.
In certain circumstances, it can happen that the shaping of the lens does not achieve a good mount in the frame at the first attempt. The operator must then perform additional machining. To do this, the lens is placed in the machine and blocked in position using the same pad, thus enabling the initial cutting-out frame of reference to be recovered.
Nevertheless, using an adhesively-bonded pad is a drawback insofar as it needs to be removed after the lens has been mounted. In addition, the lens is secured to the pad by adhesive, which means that the surface of the lens needs to be cleaned particularly thoroughly after it has been treated, thus running the risk of scratching it. Finally, these operations of applying and removing the pad are relatively complex and difficult, requiring trained and careful personnel, and they are found in practice to take time and therefore to be expensive; and for the same reason, they are difficult to automate.
Furthermore, while putting the pad into place, and more precisely while putting it into contact with the front surface of the lens, the pad is advanced with a degree of freedom in movement restricted to movement in translation only, such that the pad docks with the lens at an angle of incidence that is slightly oblique, so that putting the pad into contact with the lens leads to relative tilting. This tilting leads to an error in the positioning of the pad on the lens. This error will occur again and will thus be amplified if it becomes necessary after the pad has been removed to put the pad back into position in order to rework the lens. Repeated error in positioning the pad then leads to error that accumulates or drifts. Because of this drift in positioning, it has hitherto not been envisaged that a leans can be rework without having an accessory adhesively bonded thereto.
Depending on the organization and the equipment available to the optician, the distribution of the above-mentioned operations can extend over two or three distinct workstations. Each lens being processed needs to be transferred from one workstation to another. Inaccuracies, errors, or incidents can then occur because of the multiplicity of handling operations. Furthermore, if these operations are performed in the context of an industrial organization, there results a considerable loss of time and high production costs. Furthermore, the risk of the ophthalmic lens being damaged increases with the number of handling operations, thereby considerably lengthening delivery times and further increasing costs.
In document FR 2 825 308 or its equivalent EP 1 392 472, proposals are made to optimize the above-described process by partially automating the stages of measuring and positioning the ophthalmic lens, thus making it possible to determine the optical characteristics of the lens and to control the stage of transporting the lens to the cutting-out station and the cutting-out stage proper.
The device proposed therein has measurement means for measuring position-identifying characteristics of said lens, and means for cutting out said lens that enable the outline of the lens to be brought to the desired shape. Conventionally, those cutting-out means are constituted by an edger that has a set of grindwheels, together with blocking and rotary drive means for the lens that are constituted by two rotary shafts mounted to move axially along a common axis in order to clamp the lens on its axis between them. To move the lens towards or away from the grindwheels during machining, the clamping and drive shafts are carried by a rocker that moves transversely (in pivoting or in translation). Partial automation of the process for preparing the lens is provided by using a sliding reception and transfer carriage arranged to transfer the ophthalmic lens with two transfers between three positions, with one transfer between the measurement position in which the ophthalmic lens is presented facing measurement means, and an intermediate position that is distinct from the measurement position, and then with another transfer between said intermediate position and a cutting-out position that is distinct from the intermediate and measurement positions.
However, in that device, transferring the lens from the intermediate position to the cutting-out means is performed directly by the rocker of the edger. As a result, it is found there is a lack of flexibility in the way the rocker takes hold of the lens, thereby leading to difficulties and inaccuracies in the blocking of the lens. Unfortunately, the operation of blocking the lens is found to be particularly critical for the overall accuracy of the cutting-out operation, particularly when it is necessary to rework the lens.
Furthermore, in that device, the loading of the lens prior to measurement onto the measurement means and the unloading of the lens after being cut to shape by the operator acting on the carriage both take place without protection, at the measurement or the intermediate positions, such that loading and unloading lenses onto or from the carriage is firstly left to the initiative and goodwill of the operator (who needs to identify whether treatment of the lens is ongoing or has terminated) and secondly also requires direct access both to the measurement device, which makes it vulnerable to external attack of all kinds, and in particular to being dirtied, and also to the lens in the intermediate position in which it is nevertheless essential to ensure that the lens is not subjected to any untimely movement. Unfortunately, separating the loading position and the intermediate position would not appear to be possible without increasing the overall size of the device and degrading its performance and/or increasing its cost.
In general, it is thus possible for the operator to cause errors by untimely intervention. Furthermore, not all of the operations leading to the lens being cut out are automated, such that frequent manual intervention is required, which constitutes a source of errors and of accidents.
Consideration also needs to be taken of the fact that the rocker of the edger and in particular the chucks for blocking the lens in contact therewith, are always dirtied by a kind of sludge because of the treatment of the lenses and because material is removed therefrom, possibly together with accompanying lubrication. Since the rocker also serves to transfer the lens from the carriage to the cutting-out means and for this purpose co-operates with the transfer carriage, the transfer carriage for taking the lens to the measurement position also becomes progressively dirtied. It can thus be understood that this dirtying is very penalizing, insofar as it runs the risk of disturbing or at least degrading the optical performance of the measurement means.
It is also necessary to perform one or more feeling operations on the lens. If all of these feeling operations are performed on the edger, lenses can be treated sequentially only, without it being possible to perform feeling in parallel with cutting out since the feeler occupies the cutting-out means and makes them unavailable for their main function of cutting out.
Finally, except by complicating the mechanics of the edger rocker (with a resulting increase in cost and loss of accuracy), the lens can be taken by the edger rocker with only one degree of freedom in positioning in the plane of the lens (ignoring rotation of the shaft for blocking the lens on its axis which makes it possible to adjust the position of the lens axis, i.e. to orient the lens relative to the blocking shaft about its axis), which can be penalizing on blocking accuracy, and as a result on cutting out overall. This lack of accuracy in blocking is particularly penalizing when reworking a lens that has not been cut out properly.